Virus resistant or tolerant cells

ABSTRACT

A nucleotide sequence comprising a transcriptional regulatory sequence and a sequence contiguous therewith and under the transcriptional control thereof, which contiguous sequence encodes an RNA which consists of a plurality of sub-sequences, characterized in that at least two of the sub-sequences have the sequences of viral RNAs and the RNA contains at least one translational stop codon located upstream of the 3&#39; terminal sub-sequence. It is preferred that at least one of the sub-sequences is in an anti-sense configuration with respect to virus RNA, and that the contiguous sequence encodes mRNA. The invention also includes, inter alia, the use of such a sequence in the generation of virus resistant or tolerant plants, and such plants comprising the sequence.

The present invention relates to cells having a genetically engineered reduced susceptibility to viruses, processes for obtaining such cells, and genetic material capable of generating such reduced susceptibility. In a preferred embodiment the cells are plant cells.

Numerous attempts have been made to engineer viral resistance into plants by inserting DNA-containing vectors into acceptor plant tissue, which DNA is capable of encoding viral proteins in the thus transformed plant. The viral protein may confer resistance to an invading virus comprising a viral protein substantially the same as that encoded by the introduced DNA. Other attempts at engineering virus resistance in plants use anti-sense RNA which relies on the introduction of DNA encoding an RNA strand which is complementary to the RNA of an invading virus and thus interferes with the replication thereof. Plants displaying a broad degree of reduced susceptibility, i.e. to more than one viral type, or a greater degree of reduced susceptibility to a particular virus type, are highly desirable.

Resistance in plants to multiple virus types may be obtained by transforming plant tissue with DNA constructs made up of individual blocks of genetic elements, each element consisting essentially of three components:

(i) promoter

(ii) virus resistance conferring genetic element

(iii) terminator.

However, such constructs require the building in of many promoters and terminators and typically suffer from genetic instability.

The present invention provides inter alia, novel nucleotide sequences which can be used in the production of eukaryotic cells--particularly plant cells--which exhibit an improved resistance or tolerance to viruses. Such improvements surprisingly correlate primarily with the levels of the RNA and sub-sequences thereof encoded by the nucleotide sequence of the invention, rather than the levels of the translation products of such RNA. Indeed, improved resistance or tolerance may be obtained by transcription of the present inventive nucleotide sequences in eukaryotic cells, substantially in the absence of the translation of such transcription products.

According to the present invention there is provided a nucleotide sequence (nucleotide sequence according to the invention) comprising a transcriptional regulatory sequence and a sequence contiguous therewith and under the transcriptional control thereof, which contiguous sequence encodes an RNA which consists of a plurality of sub-sequences, characterized in that at least two of the sub-sequences have the sequences of viral RNAs and the RNA contains at least one translational stop codon located upstream of the 3' terminal sub-sequence.

Each of the sub-sequences may be responsible for conferring a reduced susceptibility to a virus in plant cells or for conferring an enhanced reduced susceptibility to a single virus type in plant cells. Such sub-sequences need not necessarily be capable of encoding protein, and it is preferred that at least one of them is incapable of encoding protein as a consequence of the RNA lacking a translational start codon at the 5' thereof and/or the contiguous sequence encoding a second sub-sequence down stream from a first sequence, the second sequence defining a translational reading frame which is out of phase with that defined by the first sub-sequence.

The said nucleotide sequence may encode an RNA having any number of sub-sequences. It is preferred that the number of sub-sequences is between 2 and 7 (inclusive) and still more preferred that the number is likewise between 2 and 4.

At least one of the sub-sequences may be in an anti-sense configuration with respect to virus RNA. The contiguous sequence may encode mRNA.

It is preferred that at least one of the sub-sequences is a cistron. By "cistron" is meant an RNA which contains a translation open reading frame, i.e. one that comprises a translation start codon, protein encoding sequence and a translation stop codon.

It is preferred that the RNA encoded by the contiguous sequence comprises at least one ribozyme (or other cleavage site) between two of the sub-sequences so that the RNA can be cleaved into regions comprising the said sub-sequences, or even into the sub-sequences per se. Except in the case of the most 5' of the sub-sequences contained within the RNA encoded by the contiguous sequence, the nucleotide sequences resulting from such cleavage will not contain a 5' cap or a ribosome binding site and will thus not be translated when present in a Eukaryotic cell.

It is more preferred that at least one of the subsequences encodes a viral coat protein or a viral nucleocapsid protein, for example, the nucleocapsid (N) protein of a tospovirus such tomato spotted wilt virus (TSWV), tomato chlorotic spot virus (TCSV), groundnut ringspot virus (GRSV), groundnut bud necrosis virus (GBNV), or Impatiens necrotic spot virus (INSV). Other viral proteins which may be encoded by the sub-sequences present in the RNA encoded by the contiguous sequence include viral replicases, movement proteins and the like derived from virus sources such as tospoviruses, potyviruses, potexviruses, tobamoviruses, luteoviruses, cucumoviruses, bromoviruses, closteorviruses, tombusviruses and furoviruses.

The invention still further provides a nucleotide sequence which is similar to the above disclosed sequence. By "similar" is meant a test sequence which is capable of hybridizing to a sequence which is complementary to the inventive nucleotide sequence. When the test and inventive sequences are double stranded the nucleic acid constituting the test sequence preferably has a TM within 20° C. of that of the inventive sequence. In the case that the test and inventive sequences are mixed together and denatured simultaneously, the TM values of the sequences are preferably within 10° C. of each other. More preferably the hybridization is performed under stringent conditions, with either the test or inventive DNA preferably being supported. Thus either a denatured test or inventive sequence is preferably first bound to a support and hybridization is effected for a specified period of time at a temperature of between 50 and 70° C. in double strength citrate buffered saline containing 0.1%SDS followed by rinsing of the support at the same temperature but with a buffer having a reduced SC concentration. Depending upon the degree of stringency required, and thus the degree of similarity of the sequences, such reduced concentration buffers are typically single strength SC containing 0.1%SDS, half strength SC containing 0.1%SDS and one tenth strength SC containing 0.1%SDS. Sequences having the greatest degree of similarity are those the hybridization of which is least affected by washing in buffers of reduced concentration. It is most preferred that the test and inventive sequences are so similar that the hybridization between them is substantially unaffected by washing or incubation in one tenth strength sodium citrate buffer containing 0.1%SDS.

The invention still further provides a nucleotide sequence which is complementary to one which hybridizes under stringent conditions with the above disclosed nucleotide sequences.

The invention also provides a DNA construct comprising the nucleotide sequence according to the invention, as well as a biological vector comprising the said sequence or construct. The biological vector may be a virus or a bacterium, such as Agrobacterium tumefaciens, for example, and the construct advantageously further encodes protein having herbicide resistance, plant growth-promoting, anti-fungal, anti bacterial, and/or anti-nematode properties.

The invention still further provides eukaryotic cells, such as plant cells (including protoplasts) for example, containing the said nucleotide sequence, construct or vector.

The invention still further provides plants comprising such plant cells, the progeny of such plants which contain the sequence stably incorporated and hereditable in a Mendelian manner, and/or the seeds of such plants or such progeny. Such plants include field crops, vegetables and fruits including tomato, pepper, melon, lettuce, cauliflower, broccoli, cabbage, brussels sprout, sugar beet, corn, sweetcorn, onion, carrot, leek, cucumber, tobacco, alfalfa, aubergine, beet, broad bean, celery, chicory, cow pea, endive, gourd, groundnut, papaya, pea, peanut, pineapple, potato, safflower, snap bean, soybean, spinach, squashes, sunflower, sorghum, water-melon and the like; and ornamental crops including Impatiens, Begonia, Petunia, Pelargonium, Viola, Cyclamen, Verbena, Vinca, Tagetes, Primula, Saint Paulia, Ageratum, Amaranthus, Anthirrhinum, Aquilegia, Chrysanthemum, Cineraria, Clover, Cosmo, Cowpea, Dahlia, Datura, Delphinium, Gerbera, Gladiolus, Gloxinia, Hippeastrum, Mesembryanthemum, Salpiglossis, Zinnia, and the like.

The invention still further provides the use of the sequence according to the invention,--whether "naked" or present in a DNA construct or biological vector--in the production of virus resistant or tolerant eukaryotic cells. By "resistant" is meant a cell which exhibits substantially no phenotypic changes as a consequence of infection with the virus. By "tolerant" is meant a cell which, although it may exhibit some phenotypic changes as a consequence of infection with a virus, does not have a substantially decreased reproductive capacity or substantially altered metabolism. Such use leads to the production of morphologically normal virus resistant or tolerant whole plants.

The invention still further provides a method of inducing resistance or tolerance to viruses in eukaryotic cells comprising introducing into such cells a nucleotide sequence according to the invention, or a construct or vector containing it. It is preferred that the cells are plant cells as indicated above.

The invention still further provides a method of inhibiting the production of at least one enzyme in a eukaryotic cell comprising introducing into the said cell a nucleotide sequence comprising a transcriptional regulatory sequence and a sequence contiguous therewith and under the transcriptional control thereof, which contiguous sequence encodes an RNA which consists of a plurality of sub-sequences, characterized in that the RNA encoded by the contiguous sequence contains at least one translational stop codon located upstream of the 3' terminal sub-sequence. In a further embodiment of the method, at least one of the sub-sequences is in an anti-sense configuration with respect to the coding sequence in the host cell mRNA which encodes the said enzyme. The enzyme may be of viral origin and present in the cell as a consequence of the viral infection thereof.

The invention will be further apparent from the following description taken in conjunction with associated drawings and sequence listings.

FIG. 1 shows a schematic representation of constructs comprising possible nucleotide sequences according to the invention, in which the contiguous sequence encodes an RNA comprising sub-sequences encoding the nucleocapsid proteins of TCSV, TWSV and GRSV.

FIG. 2 shows a schematic representation of constructs comprising possible nucleotide sequences according to the invention, in which the contiguous sequence encodes an RNA comprising sub-sequences encoding the nucleocapsid proteins of TCSV and TSWV and the coat protein of PVY.

SEQ ID No. 1 shows a DNA sequence encoding the nucleocapsid proteins of GRSV, TSWV, and TCSV; SEQ ID No. 2 shows a DNA sequence substantially similar to that given in SEQ ID No. 1, except that each of the sub-sequences encoding the nucleocapsid proteins is bordered by a ribozyme sequence rendering the RNA encoded by the DNA sequence susceptible to cleavage at pre-determined sites; SEQ ID No. 3 shows a DNA sequence encoding TCSV and TSWV nucleocapsid proteins and the coat protein of potato virus Y^(n) (PVY); SEQ ID No. 4 shows a first primer sequence designated ZUP422 (see below) and SEQ ID. No 5 shows a second primer sequence designated ZUP423 (see below).

Examples of the nucleotide sequences of the invention are provided below. These examples relate to the production of virus resistant or tolerant tomato plants. Tomato plants may be attacked by both the cucumber mosaic virus (CMV) and the tomato spotted wilt virus (TSWV). Enhanced resistance or tolerance to these viruses may be produced in a number of ways by introducing various embodiments of the nucleotide sequence of the invention into the plants, or the progenitor material thereof.

1. The contiguous sequence in the nucleotide sequence of the invention may encode an mRNA which consists--in the 5' to 3' direction--of (i) a translation start codon, (ii) the coding region of the nucleocapsid protein of TSWV, (iii) a translation stop codon, (iv) optionally a further start codon, (v) the coding region of the CMV replicase and (vi) optionally a further stop codon. When such a sequence is introduced into the cells of tomato plants, the sequence encoding the mRNA is transcribed. The region of the thus transcribed mRNA which encodes the TSWV nucleocapsid protein is translated, whilst the region of the mRNA which encodes the CMV replicase is not translated as a result of translation ceasing at the stop codon on the 3' side of the coding region of the TSWV nucleocapsid protein.

2. The contiguous sequence in the nucleotide sequence of the invention may encode an mRNA which consists--in the 5' to 3' direction--of (i) a translation start codon, (ii) the coding region of the CMV coat protein, (iii) a translation stop codon, (iv) optionally a further start codon, (v) a region encoding the nucleocapsid protein of TSWV and (vi) optionally a further stop codon. When such a sequence is introduced into the cells of tomato plants, the sequence encoding the mRNA is transcribed. The region of the thus transcribed mRNA which encodes the CMV coat protein is translated, whilst the region of the mRNA which encodes the nucleocapsid protein of TSWV is not translated as a result of translation ceasing at the stop codon on the 3' side of the region encoding the CMV coat protein.

3. The contiguous sequence in the nucleotide sequence of the invention may encode an RNA which consists--in the 5' to 3' direction--of (i) the coding region of the CMV coat protein, (ii) a translation stop codon, (iii) optionally a further start codon, (iv) a region encoding the nucleocapsid protein of TSWV and (v) optionally a further stop codon. When such a sequence is introduced into the cells of tomato plants, the sequence encoding the RNA is transcribed, but the RNA is not translated inter area because the first cistron does not contain a translation stare codon upstream of the translational stop codon, even assuming that the RNA contains a 5' cap to which ribosomes could bind. The skilled man is aware that eukaryotic cells do not translate second and subsequent cistrons in polycistronic RNA if the first cistron possesses a stop codon.

4. The contiguous sequence in the nucleotide sequence of the invention may encode an mRNA which consists--in the 5' to 3' direction--of (i) a translational start codon (ii) the coding region of the CMV coat protein, (iii) a translation stop codon, (iv) optionally a further start codon, (v) a region encoding the nucleocapsid protein of TSWV in an antisense configuration with respect to mRNA which encodes the TSWV nucleocapsid protein, (vi) optionally a further stop codon. When such a sequence is introduced into the cells of tomato plants, the sequence encoding the mRNA is transcribed. The region of the thus transcribed mRNA which encodes the CMV coat protein is translated, whilst the region of the mRNA which encodes the nucleocapsid protein of TSWV is not translated as a result of translation ceasing at the stop codon on the 3' side of the region encoding the CMV coat protein. The region of the non-translated A which contains the said anti-sense RNA is capable of base pairing with the mRNA encoding the TSWV nucleocapsid protein.

It will be appreciated that the contiguous sequence may encode an RNA comprising sub-sequences, two or more of which have sequences derived from a common virus type, so that still greater resistance to virus infection can be generated. For example:

6. The contiguous sequence in the nucleotide sequence of the invention may encode an mRNA which consists--in the 5' to 3' direction--of (i) a translational start codon (ii) the coding region of the TSWV replicase, (iii) a translation stop codon, (iv) optionally a further start codon, (v) a region encoding the nucleocapsid protein of TSWV, (vi) optionally a further stop codon. When such a sequence is introduced into the cells of tomato plants, the sequence encoding the mRNA is transcribed. The region of the thus transcribed mRNA which encodes the replicase is translated, whilst the region of the mRNA which encodes the nucleocapsid protein of TSWV is not translated as a result of translation ceasing at the stop codon on the 3' side of the region encoding the TSWV replicase.

7. The contiguous sequence in the nucleotide sequence of the invention may encode an mRNA which consists--in the 5' to 3' direction--of (i) a translational start codon (ii) a region encoding a first nucleocapsid protein of TSWV, (iii) a translation stop codon, (iv) optionally a further start codon, (v) a region encoding a second nucleocapsid protein of TSWV, (vi) optionally a further stop codon. When such a sequence is introduced into the cells of tomato plants, the sequence encoding the mRNA is transcribed. The region of the thus transcribed mRNA which encodes the first nucleocapsid protein is translated, whilst the region of the mRNA which encodes the second nucleocapsid protein is not translated as a result of translation ceasing at the stop codon on the 3' side of the region encoding the first protein. If desirable, the translational start codon on the 5' side of the region encoding the first nucleocapsid protein may be deleted.

The following discussion details the production of nucleotide sequences according to the invention, their insertion into appropriate vectors, transformation of plant material with such vectors, and the regeneration of such transformed material into virus resistant or tolerant morphologically normal whole plants.

Cultivation of plant material and bacterial strains, and generation of vectors

Cultivars of Nicotinic tabacum and Lycopersicon esculentum, used in plant transformation studies, are grown under standard greenhouse conditions. Axenic explant material is grown on standard MS media Murashige and Skoog (1962). Physiol. Plant 15:473! containing phytohormones and sucrose at appropriate concentrations.

E. coli is grown on rotary shakers at 37° C. in standard LB-medium. Agrobacterium tumefaciens strains are grown at 28° C. in Min. A medium supplemented with 0.1% glucose Ausubel et al., (1987). Current Protocols in Molecular Biology, Green Publishing Associates and Wiley Intersciences!.

In all cloning procedures, E. coli strain JM83, (F, Δ (lac-pro), ara, rpsL, .O slashed.80, dlacZM15) is used as the recipient for recombinant plasmids.

Binary vectors are conjugated to Agrobacterium tumefaciens strain LBA 4404, a strain containing the Ti-plasmid vir region, Hoekema et al. (1983) Nature 303:179 ! in standard triparental matings using E. coli HB101 containing the plasmid pRK2013 as a helper strain Figurski and Helsinki, (1979) PNAS 76:1648!. Appropriate A. tumefaciens recipients are selected on media containing rifampicin (50 μg/ml) and kanamycin (50 μg/ml).

Cloning of fragments in the vectors pUC19 Yanish-Perron et al. (1985)Gene 33:103!, pBluescript (Stratagene), pBIN19 Bevan et al. (1984) Nucl. Acids Res. 12:8711! or derivatives thereof, restriction enzyme analysis of DNA, transformation of E. coli recipient strains, isolation of plasmid DNA on small as well as large scale, nick-translation, in vitro transcription, DNA sequencing, Southern blotting and DNA gel electrophoresis are performed according to standard procedures Maniatis et al. (1982) Molecular Cloning: A Laboratory Manual. Cold Spring Harbor Laboratory, New York; Ausubel et al. supra, (1987)!.

Collection of cDNA clones to Nucleocapsid (N) genes of different tospoviruses and to the Coat Protein (CP) gene of PVY

A recombinant pUC19-derived plasmid containing the TSWV N gene is described by De Haan et al. (1990) J. Gen. Virology 71:001. Recombinant pBluescript-derived plasmids containing the TCSV N gene, and GRSV N genes are described by De Avila et al. (1993) J. Gen. Virology 74:153. A recombinant pUC19-derived plasmid containing the PVY CP gene is described by Van der Vlugt (1992). PhD thesis, Agricultural University Wageningen, The Netherlands, Ch4; pages 45-47.

Construction of expression vectors pZU-C and pZU-D

Expression vectors PZU-C and pZU-D are derivatives of pZU-B described in European patent publication No. EP-A 426 195. The unique Sma1 cloning site between the TMV Ω sequence and the NOS terminator is replaced using standard laboratory techniques Maniatis et al supr, (1982); Ausubel et al (1987) surpra! by an Nco1 cloning site, yielding pZU-C. pZU-C is linearized with Pst1 and treated with T4 DNA polymerase to obtain blunt ends. BamH1 linkers are ligated and the plasmid is digested with BamH1 and subsequently recircularized using T4 DNA ligase resulting in recombinant plasmid pZU-D.T The recombinant plasmids pZU-C and pZU-D contain the 35S HincII-TMV Ω fusion (35S-Ω), unique NcoI, Pst1 (pZU-C) or NcoI, BamHI (pZU-D) sites and the NOS terminator.

Construction of a plant transformation vector containing three tospoviral N genes

The recombinant pUC19-derived plasmid containing the GRSV N gene is linearized with BamH1 and treated with T4 DNA polymerase to obtain blunt ends. Sst1 linkers are ligated and the plasmid is digested with Sst1 and subsequently recircularized using T4 DNA ligase. The resulting plasmid is then linearized with Kpn1 and treated with T4 DNA polymerase to obtain blunt ends. BamH1 linkers are ligated and the plasmid is digested with BamH1 and subsequently recircularized using T4 DNA ligase resulting in recombinant plasmid GRSV N (FIG. 1), containing the GRSV N gene (nucleotides 1986 through to 2953 SEQ ID No. 1). Plasmid GRSV N is subjected to Sst1 digestion and the fragment containing the GRSV N gene is separated electrophoretically and purified from the gel using an NA-45 (Schleicher and Schull) DEAE membrane and cloned into Sst1 linearized TCSV N (a pBluescript-derived recombinant plasmid) containing the TCSV N gene (nucleotides 7 through to 981 SEQ ED No. 1) resulting in TCSV N--GRSV N. Plasmid TSWV N is subjected to Kpn1 digestion and the fragment containing the TSWV N gene (nucleotides 988 through to 1930 SEQ ID No. 1) is separated electrophoretically and purified from the gel using an NA45 DEAE membrane and cloned into Kpn1 linearized TCSV N--GRSV N, resulting in the recombinant plasmid TCSV N--TSWV N--GRSV N (FIG. 1) Plasmid TCSV N--TSWV N--GRSV N (SEQ ID No. 1) is subjected to BamH 1 digestion and the fragment containing the tospoviral N genes, is separated electrophoretically and purified from the gel using an NA45 DEAE membrane and cloned into BamH1 linearized pZU-D, resulting in pTOSPON 1 (FIG. 1). The nucleotide sequence containing the 35S-Ω promoter, the tosporival N genes and the NOS terminator is excised from the plasmid pTOSPON 1 via a partial Sst1 digestion. The isolated gene cassette is then inserted into the Sst1 linearized pBIN19 to create the binary transformation vector pBIN-TOSPON 1.

Construction of a plant transformation vector containing three tospoviral N genes flanked by ribozyme sequences

The nucleotide sequence of DNA encoding the RNA which encodes the three tospoviral nucleocapsid sequences contains ribozyme sequences and is depicted in SEQ ID No. 2.

Two primers are constructed, ZUP422 (depicted in SEQ ID No. 4) and ZUP423 (depicted in SEQ ID No. 5) containing Kpn1 cloning sites, the active ribozyme sequence of the tobacco ringspot virus satellite RNA and 17 nucleotides overlap to the coding region of the TSWV N gene. The primers are used to PCR amplify the TSWV N gene using pTOSPON as a template. The PCR fragment is made blunt-ended by treatment with T4 DNA polymerase and subsequently cloned in the EcoR V site of plasmid pSK+. Clones are obtained, which contain a Kpn1 insertion of the expected size. Sequence analysis reveals that the Kpn1 site originating from primer ZUP422 is destroyed. Therefore, the Kpn1 site located on the multilinker of pSK+, together with the Kpn1 site originating from primer ZUP423 are used to replace the TSWV N gene (as a Kpn 1 fragment) located on the recombinant plasmid TCSV N--TSWV N GRSV N (see above), yielding plasmids TCSV N--ribozyme--TSWV N--ribozyme--GRSV N and TCSV N--ribozyme--TSWV N antisense--ribozyme--GRSV N. These plasmids are linearized with BamH1 and used as templates to produce run-off transcripts with T7 RNA polymerase. Polyacrylamide gel electrophoresis reveals that the primary transcripts are immediately and completely cleaved to yield the separate sense and/or tospoviral N gene molecules. Plasmids TCSV N--ribozyme--TSWV N--ribozyme--GRSV N and TCSV N--ribozyme--TSWV N antisense--ribozyme--GRSV N (SEQ ID No. 2) are subjected to BamH1 digestion and the fragments containing the tospoviral N genes are separated electrophoretically and purified from the gel using an NA-45 DEAE membrane and cloned into BamH1 linearized pZU-D, resulting in pTOSPON-ribo1 and pTOSPON-ribo2 (FIG. 1) respectively. The nucleotide sequences containing the 35S-Ω promoter, the tosporival N genes bordered by ribozymes, and the NOS terminator are excised from the plasmids via a partial Sst1 digestion. The isolated gene cassettes are then inserted into the Sst1 linearized pBIN19 to create the binary transformation vectors pBIN-TOSPON-ribo1 and pBIN-TOSPON-ribo2 respectively.

Both constructs are transferred to plants yielding 23 pBIN-TOSPON-ribo1 and 17 pBIN-TOSPON-ribo2 transformants. The progeny of the transformants is challenged with the various tospoviruses and found to exhibit an improved resistance or tolerance thereto, in comparison with non-transformed controls.

Construction of a plant transformation vector containing two tosporival N genes and the CP gene of PVY

Plasmid TCSV N is subjected to digestion with Pst1 and the large fragment containing the TCSV N gene and pUC19 is separated electrophoretically and purified from the gel using a DEAE membrane (NA-45, Schleicher and Schull) and recircularized using T4 DNA ligase, resulting in TCSV N (FIG. 2). The recombinant pUC19-derived plasmid containing the pVY CP gene (nucleotides 1984 through to 2899 SEQ ID No. 3) is linearized with Sph1 and treated with T4 DNA polymerase to obtain blunt ends. Sst1 linkers are ligated and the plasmid is digested with Sst1 and subsequently re-circularized using T4 DNA ligase, resulting in recombinant plasmid PVY CP (FIG. 2). Plasmid PVY CP is subjected to Sst1 digestion and the fragment containing the PVY CP gene is separated electrophoretically and purified from the gel using an NA-45 DEAE membrane and cloned into Sst1 linearized TCSV N, resulting in TCSV N-PVY CP. Plasmid TSWV N is subjected to Kpn1 digestion and the fragment containing the TSWV N gene (FIG. 2) is separated electrophoretically and purified from the gel using an NA-45 DEAE membrane and cloned into Kpn1 linearized TCSV N--PVY CP, resulting in the recombinant plasmid TCSV N--TSWV N--PVY CP. Plasmid TCSV N--TSWV N--PVY CP is subjected to Pst1 digestion and the fragment containing the tospoviral N genes and the PVY CP gene is separated electrophoretically and purified from the gel using an NA-45 DEAE membrane and cloned into Pst1 linearized pZU-C, resulting in pTOSPOPVY 1 (FIG. 2). The gene cassette containing the 35S-Ω promoter, TCSV and TSWV N genes, the PVY CP gene and the NOS terminator is excised from the plasmid pTOSPOPVY 1 via a partial Sst1 digestion. The isolated gene cassette is then inserted into the Sst1 linearized pBIN19 to create the binary transformation vector pBIN-TOSPOPVY 1.

Introduction of binary vectors to tobacco and tomato plant material

Methods to transfer binary vectors to plant material are known to a person skilled in the art. Variations in procedures exist due to differences in Agrobacterium strains used, different sources of explant material, differences in regeneration systems, and on the cultivar of plant species employed.

Binary plant transformation vectors as described above are employed in plant transformation experiments according to the following procedures. Binary vector constructs are transferred by tri-parental mating to an acceptor Agrobacterium tumefaciens strain, followed by southern analysis of exconjugants for verification of proper transfer of the construct to the acceptor strain, inoculation and cocultivation of axenic explant material with Agrobacterium tumefaciens strain of choice, selective killing of the Agrobacterium tumefaciens used with appropriate antibiotics, selection of transformed cells by growing on selective media containing kanamycin, transfer of tissue to shoot-inducing media, transfer of selected shoots to root induction media, transfer of plantlets to soil, assaying for intactness of the construct by southern analyses of isolated total DNA from the transgenic plant, assaying for proper function of the inserted gene by northern analysis and/or enzyme assays and western blot analysis of proteins following methods as described by Ausubel et al. supra.

Expression of DNA sequences in tobacco and tomato plant cells

RNA is extracted from leaves of regenerated plants using the following protocol. 200 mg leaf material is ground to a fine powder in liquid nitrogen. 800 μl RNA extraction buffer (100 mM Tris-HC1 (pH 8,0), 500 mM NaCl, 2 mM EDTA, 200 nM β-Mercapto-ethanol, 0.4% SDS) is added and the homogenate extracted with phenol, and nucleic acids collected by alcohol precipitation. Nucleic acids are re-suspended in 0.5 ml 10 MM Tris-HCl (pH 8,0), 1 mM EDTA, and LiCl is added to a final concentration of 2 M, and left on ice for no longer than 4 hours. The RNA is collected by centrifugation and re-suspended in 400 μl 10 mM Tris-HCl (pH 8.0), 1 mM EDTA and then precipitated with alcohol. The RNA is then re-suspended in 50 μl 10 mM Tris-HCl (pH 8,0), 1 mM EDTA. PNAs are separated on glyoxal/agarose gels and blotted to Genescreen as described by van Grinsven et al. (1986) Theor. Appl. Gen. 73:94-101!. Recombinant viral RNA sequences are detected using DNA or RNA probes labeled with ³² P!, ³⁵ S! or by using non-radioactive labeling techniques. Based on northern analysis, it is determined to what extent the regenerated plants express recombinant viral genes.

Plants transformed with recombinant viral DNA molecules are also subjected to Western blot analysis after inoculation of the plant with the respective virus. Proteins are extracted from leaves of transformed plants by grinding in sample buffer Laemmli (1970) Nature 244:29! and a 50 μg portion of protein is subjected to electrophoresis in a 12.5% SDS-polyacrylamide gel. Separated proteins are transferred to nitrocellulose electrophoreteically as described by Towbin et al. (1979) PNAS76:4350!. Transferred proteins are reacted with anti-serum raised against purified TCSV nucleocapsids. Based on the results of the Western analysis it is determined that transformed plants express TCSV protein.

Resistance of tobacco and tomato plants against tospoviral and/or potyviral infection

Transformed plants are grown in the greenhouse under standard quarantine conditions in order to prevent any infections by undesirable pathogens. The transformants are self-pollinated and the seeds harvested. Progeny plants are analyzed for segregation of the inserted gene and are subsequently infected with TCSV, TSWV, and/or GRSV and PVY by mechanical inoculation. Tissue from plants systemically inected with these viruses is ground in 5 volumes of ice-cold inoculation buffer (10 mM phosphate buffer, containing 10 mM sodium sulphite) and rubbed in the presence of carborundum power on the first two fully extended leafs of approximately 5 week old seedlings. Inoculated plants are monitored for symptom development for 3 weeks after inoculation.

Plants containing TOSPON 1 (FIG. 1), pTOSPON-ribo1, pTOSPON-ribo2 or TOSPOPVY 1 (FIG. 2) sequences show reduced susceptibility to infection with TCSV, TSWV, and/or GRSV and PVY compared with untransformed control plants which show severe systemic symptoms within 7 days after inoculation with these viruses. Plants that resisted infection are self pollinated and the like resistance of the resulting S2 progeny is demonstrated.

It will be appreciated that the present invention is not limited to the above examples only, but includes all logical and obvious extensions of the embodiments of the invention disclosed herein as well as those specifically claimed. Thus the invention also includes the embodiments indicated in the next paragraph in the clauses numbered 1-12.

(1). Multigene DNA constructs comprising at least one non-structural gene wherein the multigene DNA is under the control of a single set of genetic regulatory elements. By "non-structural gene" is meant a gene capable of coding for a viral RNA molecule which is substantially incapable of encoding for a viral polypeptide or protein but which is nevertheless capable of conferring an RNA mediated reduced susceptibility of a plant virus in plant cells. (2). Constructs according to clause 1, wherein the at least one non-structural gene is a viral gene. (3). Multigene DNA constructs comprising at least one non-structural gene wherein the multigene DNA constructs are capable of giving rise to viral elements in plant cells which are capable of conferring a reduced susceptibility to plant viruses in plant cells, and wherein the multigene DNA is under the control of a single set of genetic regulatory elements. (4) Constructs according to clauses 2 to 3 comprising at least one viral non-structural gene and one viral structural gene. (5) Constructs according to any one of clauses 2 to 4 comprising at least two non-structural genes and no viral structural gene elements. (6). Constructs according to clause 5 comprising from 2 to 5 viral non-structural genes. (7). Constructs according to any one of clauses 1 to 3 comprising DNA capable of coding for viral RNA molecules of tospoviruses, potyviruses, potexviruses, tobamoviruses, luteoviruses, cucumoviruses, bromoviruses, closteroviruses, tombusviruses, and furoviruses. (8) Constructs according to clause 7, wherein the DNA codes for non-structural viral RNA molecules of nucleocapsid proteins, viral coat proteins, and non-structural viral proteins. (9). Plants comprising multigene DNA constructs of any one of clauses 1 to 3. (10). Plants according to clause 9 selected from the group comprising tomatoes, peppers, melons, lettuces, caulifowers, broccolis, cabbages, brussels sprouts, sugar beet, corn (maize), sweetcorn, onions, carrots, leeks, cucumbers, tobacco's alfalfa's, aubergines, beets, broad beans, celery's, chicory's, cow peas, endives, gourds, groundnuts, papayas, peas, peanuts, pineapples, potatoes, safflowers, snap beans, soybeans, spinaches, squashes, sunflowers, water-melons, and sorghums. (11). Plants according to clause 9 selected from the group ornamentals consisting essentially of Impatiens, IBegonias, Petumias, Pelargoniums (geraniums), Violas, Cyclamens, Verbenas, Vincas, Tagetes, Primulas, Saint Paulia's Ageratums, Amaranthuses, Anthirrhinums, Aquilegias, Chrysanthemums, Cineraria, Clovers, Cosmos's, Cowpeas, Dahlia's, Daturas, Delphiniums, Gerbera's, Gladioluses, Gloxinias, Hippeastrums, Mesembryanthemums, Salpiglossis, and Zinnias. (12). A method for obtaining plants displaying a reduced susceptibility to viruses which comprises: (a) inserting into the genome of a plant cell a DNA construct according to any one of clauses 1 to 8; (b) obtaining transformed cells; and (c) regenerating from the transformed cells genetically transformed plants.

    __________________________________________________________________________     #             SEQUENCE LISTING     - (1) GENERAL INFORMATION:     -    (iii) NUMBER OF SEQUENCES: 5     - (2) INFORMATION FOR SEQ ID NO:1:     -      (i) SEQUENCE CHARACTERISTICS:     #pairs    (A) LENGTH: 2959 base               (B) TYPE: nucleic acid               (C) STRANDEDNESS: double               (D) TOPOLOGY: unknown     -    (iii) HYPOTHETICAL: NO     -    (iii) ANTI-SENSE: NO     -     (vi) ORIGINAL SOURCE:     #sequence (A) ORGANISM: Chimeric     -     (xi) SEQUENCE DESCRIPTION: SEQ ID NO:1:     - GGATCCTGCA GAGCAATTGT GTCAATTTTA TTCAAAAACC TAATACTCAG CA - #ATACAAAT       60     - CATCACATTA ACAGGATAAG TAACGACCGC GGTCTACAGT GTTGCACTTT CT - #CACCTTGA      120     - ATCTTATCTC TCGAGAAAGG TCTAGATCTA AACTACCACC ATGTCTAAGG TC - #AAGCTCAC      180     - AAAAGAAAAC ATTGTCTCTC TTTTGACTCA ATCTGAGGAT GTTGAGTTTG AA - #GAAGACCA      240     - GAACCAGGTT GCATTCAACT TTAAGACTTT TTGTCAGGAA AATCTTGACC TG - #ATTAAGAA      300     - AATGAGTATC ACTTCATGTT TGACTTTCTT GAAGAATCGC CAAAGCATCA TG - #AAAGTTGT      360     - GAAACAAAGT GATTTTACTT TTGGCAAGGT CACGATAAAG AAAAATTCAG AG - #AGGGTTGA      420     - AGCTAAAGAC ATGACTTTCA GAAGGCTTGA TAGCATGATA AGAGTGAAAC TC - #ATAGAAGA      480     - GACTGCAAAC AATGAGAATC TTGCTATCAT CAAGGCAAAA ATTGCCTCCC AT - #CCTTTGGT      540     - CCAAGCTTAC GGGCTGCCTT TGGACGATGC AAAATCTGTG AGACTTGCCA TA - #ATGCTTGG      600     - AGGTAGTATC CCTCTCATTG CTTCTGTTGA CAGTCTCGAA ATGATCAGTG TT - #GTTCTTGC      660     - CATATATCAA GATAGTCAAG TACAGGAGTT AGGGATTGAA CCAACTAAGT AC - #AACACTAA      720     - GGAAGCTCTG GGGAAGGTTT GCACTGTGCT GAAAAGCAAA GGATTTACAA TG - #GATGATGC      780     - ACAAGATAAC AAAGGGAAAG AATATGCTAA GATACTCAGT TCTTGCAATC CC - #AATGCTAA      840     - GGGAAGCATT GCTATGGACT ATTACAGTGA CAATCTTGAG AAGTTCTATG AA - #ATGTTTGG      900     - AGTCAAGAAA GAGGCCAAGA TTGCTGGTGT TGCATAAAAG CTTCTTTGTG TT - #AATTAAGA      960     - GATGCATAAT ACTAAGTGTG GGGTACCCTT AACACTCAGT CTTACAAATC AT - #CACATTAA     1020     - GAACCTAAGA AACGACTGCG GGATACAGAG TTGCACTTTC GCACCTTGAG TT - #ACATACGG     1080     - TCAAAGCATA TAACAACTTT TACGATCATC ATGTCTAAGG TTAAGCTCAC TA - #AGGAAAGC     1140     - ATTGTTGCTT TGTTGACACA AGGCAAAGAC CTTGAGTTTG AGGAAGATCA GA - #ATCTGGTA     1200     - GCATTCAACT TCAAGACTTT TTGTCTGGAA AACATCGACC AGATCAAGAA GA - #TGAGCGTT     1260     - ATTTCATGTC TGACATTCCT AAAGAATCGT CAGAGCATAA TGAAGGTTAT TA - #AGCAAAGC     1320     - GATTTTACTT TTGGTAAAAT TACCATAAAG AAAACTTCAG ACAGGATTGG AG - #GCACTGAC     1380     - ATGACCTTCA GAAGGCTTGA TAGCTTGATC AGGGTCAGGC TTGTTGAAGA AA - #CTGGGAAT     1440     - TCTGAGAATC TCAATACTAT CAAATCTAAG ATTGCTTCCC ATCCTTTGAT TC - #AAGCCTAT     1500     - GGATTACCTC TCGATGATGC AAAGTCTGTG AGACTTGCCA TAATGCTGGG AG - #GTAGCTTA     1560     - CCTCTTATTG CTTCAGTTGA TAGCTTTGAG ATGATCAGTG TTGTCTTGGC TA - #TATATCAG     1620     - GATGCAAAAT ACAAGGACCT CGGGATCGAC CCAAAGAAGT ATGACACCAA GG - #AAGCCTTA     1680     - GGAAAAGTTT GCACTGTGCT GAAAAGCAAA GCATTTGAAA TGAATGAAGA TC - #AGGTGAAG     1740     - AAGGGGAAAG AGTATGCTGC TATACTTAGC TCCAGCAATC CTAATGCTAA AG - #GGAGTGTT     1800     - GCTATGGAAC ATTACAGTGA AACTCTTAAC AAGTTCTATG AAATGTTCGG GG - #TTAAAAAG     1860     - CAGGCAAAAC TCGCAGAACT TGCTTGAAAG CAGCTGTAAG TTAAATTATA AA - #AAAGCCTA     1920     - TAAATATATA AAGCTTATCG ATACCGTCGA CCTCGAGGGG GGGCCCGGTA CC - #GAGCTCGC     1980     - TGCAGAGCAA TTGTGTCAAT TTTATTCAAA AACATACTAC TCAGCAACAC AA - #ATCATCAC     2040     - ATTGCCAGGA TAAGTAACGA CTGCGGTCTA CAGAGTCGTA CTTTCTTACC TT - #GAATCACA     2100     - TCTCTCGAGA GCGGTCTAGA TCTACACTGC CAAAAATGTC TAAGGTCAAG CT - #CACCAGAG     2160     - AGAACATTAT CTCTCTTCTA ACTCAGGCTG GAGAAATCGA GTTTGAAGAA GA - #TCAAATCA     2220     - AGGCTACATT CAACTTCGAA GACTTTTGCG GAGAAAATCT TGATTCAATC AA - #GAAAATGA     2280     - GCATTACCTC ATGTTTGACT TTCCTGAAAA ATCGCCAGAG CATCATGAAA GT - #TGTGAACC     2340     - TTTGTGATTT TACCTTTGGG AAAATCACAA TCAAAAAGAA TTCTGGAAGG GT - #TGGAGCTA     2400     - ATGATATGAC TTTCAGAAGG CTTGATAGCA TGATAAGAGT TAAGCTGATT GA - #AGAAACTG     2460     - GAAAAGCAGA AAACCTTGCT ATTATCAAGT CTAAGATTGC CTCTCATCCT CT - #TGTTCAAG     2520     - CTTATGGTCT GCCTCTGACA GATGCAAAGT CTGTAAGGCT TGCCATAATG CT - #AGGAGGTA     2580     - GTATCCCTCT GATTGCTTCT GTGGACAGCT TTGAAATGAT CAGCATCATC CT - #TGCCATAT     2640     - ACCAAGATGC TAAATATAAA GATCTTGGAA TTGAACCTTC GAAGTATAAC AC - #TAAAGAAG     2700     - CTTTAGGAAA AGTCTGCACT GTGCTGAAAA GCAAAGGATT TACAATGGAT GA - #AGAGCAAG     2760     - TGCAGAAAGG GAAAGAATAT GCTACAATAC TCAGCTCTTG CAATCCTAAT GC - #TAAAGGAA     2820     - GCATTGCTAT GGAACATTAC AGTGAGCATC TTGACAAATT CTATGCAATG TT - #CGGAGTAA     2880     - GGAAAGAAGC CAAAATTTCA GGTGTTGCAT GAAAGCTTCT TAAAATCTAT TT - #AAGAGATG     2940     #                 295 - #9     - (2) INFORMATION FOR SEQ ID NO:2:     -      (i) SEQUENCE CHARACTERISTICS:     #pairs    (A) LENGTH: 2899 base               (B) TYPE: nucleic acid               (C) STRANDEDNESS: double               (D) TOPOLOGY: unknown     -    (iii) HYPOTHETICAL: NO     -    (iii) ANTI-SENSE: NO     -     (vi) ORIGINAL SOURCE:     #sequence (A) ORGANISM: Chimeric     -     (xi) SEQUENCE DESCRIPTION: SEQ ID NO:2:     - GGATCCTGCA GAGCAATTGT GTCAATTTTA TTCAAAAACC TAATACTCAG CA - #ATACAAAT       60     - CATCACATTA ACAGGATAAG TAACGACCGC GGTCTACAGT GTTGCACTTT CT - #CACCTTGA      120     - ATCTTATCTC TCGAGAAAGG TCTAGATCTA AACTACCACC ATGTCTAAGG TC - #AAGCTCAC      180     - AAAAGAAAAC ATTGTCTCTC TTTTGACTCA ATCTGAGGAT GTTGAGTTTG AA - #GAAGACCA      240     - GAACCAGGTT GCATTCAACT TTAAGACTTT TTGTCAGGAA AATCTTGACC TG - #ATTAAGAA      300     - AATGAGTATC ACTTCATGTT TGACTTTCTT GAAGAATCGC CAAAGCATCA TG - #AAAGTTGT      360     - GAAACAAAGT GATTTTACTT TTGGCAAGGT CACGATAAAG AAAAATTCAG AG - #AGGGTTGA      420     - AGCTAAAGAC ATGACTTTCA GAAGGCTTGA TAGCATGATA AGAGTGAAAC TC - #ATAGAAGA      480     - GACTGCAAAC AATGAGAATC TTGCTATCAT CAAGGCAAAA ATTGCCTCCC AT - #CCTTTGGT      540     - CCAAGCTTAC GGGCTGCCTT TGGACGATGC AAAATCTGTG AGACTTGCCA TA - #ATGCTTGG      600     - AGGTAGTATC CCTCTCATTG CTTCTGTTGA CAGTCTCGAA ATGATCAGTG TT - #GTTCTTGC      660     - CATATATCAA GATAGTCAAG TACAGGAGTT AGGGATTGAA CCAACTAAGT AC - #AACACTAA      720     - GGAAGCTCTG GGGAAGGTTT GCACTGTGCT GAAAAGCAAA GGATTTACAA TG - #GATGATGC      780     - ACAAGATAAC AAAGGGAAAG AATATGCTAA GATACTCAGT TCTTGCAATC CC - #AATGCTAA      840     - GGGAAGCATT GCTATGGACT ATTACAGTGA CAATCTTGAG AAGTTCTATG AA - #ATGTTTGG      900     - AGTCAAGAAA GAGGCCAAGA TTGCTGGTGT TGCATAAAAG CTTCTTTGTG TT - #AATTAAGA      960     - GATGCATAAT ACTAAGTGTG GGGTACCGGG CCCCCCCTCG AGGTCGACGG TA - #TCGATAAG     1020     - CTTGATGTAC AGTCACCGGA TGTGCTTTCC GGTCTGATGA GTCCGTGAGG AC - #GAAACGGT     1080     - ATGGTCTAAG GTTAAGCTCA CTAAGGAAAG CATTGTTGCT TTGTTGACAC AA - #GGCAAAGA     1140     - CCTTGAGTTT GAGGAAGATC AGAATCTGGT AGCATTCAAC TTCAAGACTT TT - #TGTCTGGA     1200     - AAACATCGAC CAGATCAAGA AGATGAGCGT TATTTCATGT CTGACATTCC TA - #AAGAATCG     1260     - TCAGAGCATA ATGAAGGTTA TTAAGCAAAG CGATTTTACT TTTGGTAAAA TT - #ACCATAAA     1320     - GAAAACTTCA GACAGGATTG GAGGCACTGA CATGACCTTC AGAAGGCTTG AT - #AGCTTGAT     1380     - CAGGGTCAGG CTTGTTGAAG AAACTGGGAA TTCTGAGAAT CTCAATACTA TC - #AAATCTAA     1440     - GATTGCTTCC CATCCTTTGA TTCAAGCCTA TGGATTACCT CTCGATGATG CA - #AAGTCTGT     1500     - GAGACTTGCC ATAATGCTGG GAGGTAGCTT ACCTCTTATT GCTTCAGTTG AT - #AGCTTTGA     1560     - GATGATCAGT GTTGTCTTGG CTATATATCA GGATGCAAAA TACAAGGACC TC - #GGGATCGA     1620     - CCCAAAGAAG TATGACACCA AGGAAGCCTT AGGAAAAGTT TGCACTGTGC TG - #AAAAGCAA     1680     - AGCATTTGAA ATGAATGAAG ATCAGGTGAA GAAGGGGAAA GAGTATGCTG CT - #ATACTTAG     1740     - CTCCAGCAAT CCTAATGCTA AAGGGAGTGT TGCTATGGAA CATTACAGTG AA - #ACTCTTAA     1800     - CAAGTTCTAT GAAATGTTCG GGGTTAAAAA GCAGGCAAAA CTCGCAGAAC TT - #GCTTGACC     1860     - GTCACCGGAT GTGCTTTCCG GTCTGATGAG TCCGTGAGGA CGAAACGGTA CC - #GAGCTCGC     1920     - TGCAGAGCAA TTGTGTCAAT TTTATTCAAA AACATACTAC TCAGCAACAC AA - #ATCATCAC     1980     - ATTGCCAGGA TAAGTAACGA CTGCGGTCTA CAGAGTCGTA CTTTCTTACC TT - #GAATCACA     2040     - TCTCTCGAGA GCGGTCTAGA TCTACACTGC CAAAAATGTC TAAGGTCAAG CT - #CACCAGAG     2100     - AGAACATTAT CTCTCTTCTA ACTCAGGCTG GAGAAATCGA GTTTGAAGAA GA - #TCAAATCA     2160     - AGGCTACATT CAACTTCGAA GACTTTTGCG GAGAAAATCT TGATTCAATC AA - #GAAAATGA     2220     - GCATTACCTC ATGTTTGACT TTCCTGAAAA ATCGCCAGAG CATCATGAAA GT - #TGTGAACC     2280     - TTTGTGATTT TACCTTTGGG AAAATCACAA TCAAAAAGAA TTCTGGAAGG GT - #TGGAGCTA     2340     - ATGATATGAC TTTCAGAAGG CTTGATAGCA TGATAAGAGT TAAGCTGATT GA - #AGAAACTG     2400     - GAAAAGCAGA AAACCTTGCT ATTATCAAGT CTAAGATTGC CTCTCATCCT CT - #TGTTCAAG     2460     - CTTATGGTCT GCCTCTGACA GATGCAAAGT CTGTAAGGCT TGCCATAATG CT - #AGGAGGTA     2520     - GTATCCCTCT GATTGCTTCT GTGGACAGCT TTGAAATGAT CAGCATCATC CT - #TGCCATAT     2580     - ACCAAGATGC TAAATATAAA GATCTTGGAA TTGAACCTTC GAAGTATAAC AC - #TAAAGAAG     2640     - CTTTAGGAAA AGTCTGCACT GTGCTGAAAA GCAAAGGATT TACAATGGAT GA - #AGAGCAAG     2700     - TGCAGAAAGG GAAAGAATAT GCTACAATAC TCAGCTCTTG CAATCCTAAT GC - #TAAAGGAA     2760     - GCATTGCTAT GGAACATTAC AGTGAGCATC TTGACAAATT CTATGCAATG TT - #CGGAGTAA     2820     - GGAAAGAAGC CAAAATTTCA GGTGTTGCAT GAAAGCTTCT TAAAATCTAT TT - #AAGAGATG     2880     #                 289 - #9     - (2) INFORMATION FOR SEQ ID NO:3:     -      (i) SEQUENCE CHARACTERISTICS:     #pairs    (A) LENGTH: 2917 base               (B) TYPE: nucleic acid               (C) STRANDEDNESS: double               (D) TOPOLOGY: unknown     -    (iii) HYPOTHETICAL: NO     -    (iii) ANTI-SENSE: NO     -     (vi) ORIGINAL SOURCE:     #sequence (A) ORGANISM: Chimeric     -     (xi) SEQUENCE DESCRIPTION: SEQ ID NO:3:     - CTGCAGAGCA ATTGTGTCAA TTTTATTCAA AAACATACTA CTCAGCAACA CA - #AATCATCA       60     - CATTGCCAGG ATAAGTAACG ACTGCGGTCT ACAGAGTCGT ACTTTCTTAC CT - #TGAATCAC      120     - ATCTCTCGAG AGCGGTCTAG ATCTACACTG CCAAAAATGT CTAAGGTCAA GC - #TCACCAGA      180     - GAGAACATTA TCTCTCTTCT AACTCAGGCT GGAGAAATCG AGTTTGAAGA AG - #ATCAAATC      240     - AAGGCTACAT TCAACTTCGA AGACTTTTGC GGAGAAAATC TTGATTCAAT CA - #AGAAAATG      300     - AGCATTACCT CATGTTTGAC TTTCCTGAAA AATCGCCAGA GCATCATGAA AG - #TTGTGAAC      360     - CTTTGTGATT TTACCTTTGG GAAAATCACA ATCAAAAAGA ATTCTGGAAG GG - #TTGGAGCT      420     - AATGATATGA CTTTCAGAAG GCTTGATAGC ATGATAAGAG TTAAGCTGAT TG - #AAGAAACT      480     - GGAAAAGCAG AAAACCTTGC TATTATCAAG TCTAAGATTG CCTCTCATCC TC - #TTGTTCAA      540     - GCTTATGGTC TGCCTCTGAC AGATGCAAAG TCTGTAAGGC TTGCCATAAT GC - #TAGGAGGT      600     - AGTATCCCTC TGATTGCTTC TGTGGACAGC TTTGAAATGA TCAGCATCAT CC - #TTGCCATA      660     - TACCAAGATG CTAAATATAA AGATCTTGGA ATTGAACCTT CGAAGTATAA CA - #CTAAAGAA      720     - GCTTTAGGAA AAGTCTGCAC TGTGCTGAAA AGCAAAGGAT TTACAATGGA TG - #AAGAGCAA      780     - GTGCAGAAAG GGAAAGAATA TGCTACAATA CTCAGCTCTT GCAATCCTAA TG - #CTAAAGGA      840     - AGCATTGCTA TGGAACATTA CAGTGAGCAT CTTGACAAAT TCTATGCAAT GT - #TCGGAGTA      900     - AGGAAAGAAG CCAAAATTTC AGGTGTTGCA TGAAAGCTTC TTAAAATCTA TT - #TAAGAGAT      960     - GAGTATTGTA GGGTACCCTT AACACTCAGT CTTACAAATC ATCACATTAA GA - #ACCTAAGA     1020     - AACGACTGCG GGATACAGAG TTGCACTTTC GCACCTTGAG TTACATACGG TC - #AAAGCATA     1080     - TAACAACTTT TACGATCATC ATGTCTAAGG TTAAGCTCAC TAAGGAAAGC AT - #TGTTGCTT     1140     - TGTTGACACA AGGCAAAGAC CTTGAGTTTG AGGAAGATCA GAATCTGGTA GC - #ATTCAACT     1200     - TCAAGACTTT TTGTCTGGAA AACATCGACC AGATCAAGAA GATGAGCGTT AT - #TTCATGTC     1260     - TGACATTCCT AAAGAATCGT CAGAGCATAA TGAAGGTTAT TAAGCAAAGC GA - #TTTTACTT     1320     - TTGGTAAAAT TACCATAAAG AAAACTTCAG ACAGGATTGG AGGCACTGAC AT - #GACCTTCA     1380     - GAAGGCTTGA TAGCTTGATC AGGGTCAGGC TTGTTGAAGA AACTGGGAAT TC - #TGAGAATC     1440     - TCAATACTAT CAAATCTAAG ATTGCTTCCC ATCCTTTGAT TCAAGCCTAT GG - #ATTACCTC     1500     - TCGATGATGC AAAGTCTGTG AGACTTGCCA TAATGCTGGG AGGTAGCTTA CC - #TCTTATTG     1560     - CTTCAGTTGA TAGCTTTGAG ATGATCAGTG TTGTCTTGGC TATATATCAG GA - #TGCAAAAT     1620     - ACAAGGACCT CGGGATCGAC CCAAAGAAGT ATGACACCAA GGAAGCCTTA GG - #AAAAGTTT     1680     - GCACTGTGCT GAAAAGCAAA GCATTTGAAA TGAATGAAGA TCAGGTGAAG AA - #GGGGAAAG     1740     - AGTATGCTGC TATACTTAGC TCCAGCAATC CTAATGCTAA AGGGAGTGTT GC - #TATGGAAC     1800     - ATTACAGTGA AACTCTTAAC AAGTTCTATG AAATGTTCGG GGTTAAAAAG CA - #GGCAAAAC     1860     - TCGCAGAACT TGCTTGAAAG CAGCTGTAAG TTAAATTATA AAAAAGCCTA TA - #AATATATA     1920     - AAGCTTATCG ATACCGTCGA CCTCGAGGGG GGGCCCGGTA CCGAGCTCGG TA - #CCCGGGGA     1980     - TCCACCATGG GAAATGACAC AATCGATGCA GGAGGAAGCA CTAAGAAAGA TG - #CAAAACAA     2040     - GAGCAAGGTA GCATTCAACC AAATCTCAAC AAGGAAAAGG TAAAGGACGT GA - #ATGTTGGA     2100     - ACATCTGGAA CTCACACTGT GCCACGAATT AAAGCTATCA CGTCCAAAAT GA - #GAATGCCC     2160     - AAGAGTAAGG GTGCAACTGT ACTAAATTTG GAACACCTAC TCGAGTATGC TC - #CACAGCAA     2220     - ATTGAAATCT CAAATACTCG AGCAACTCAA TCACAGTTTG ATACATGGTA TG - #AAGCAGTA     2280     - CAACTTGCAT ACGACATAGG AGAAACTGAA ATGCCAACTG TGATGAATGG GC - #TTATGGTT     2340     - TGGTGCATTG AAAATGGAAC CTCGCCAAAT ATCAATGGAG TTTGGGTTAT GA - #TGGATGGA     2400     - GATGAACAAG TCGAATACCC AGTGAAACCA ATCGTTGAGA ATGCAAAACC AA - #CACTTAGG     2460     - CAAATCATGG CACATTTCTC AGATGTTGCA GAAGCGTATA TAGAAATGCG CA - #ACAAAAAG     2520     - GAACCATATA TGCCACGATA TGGTTTAGTT CGTAATCTGC GCGATGGAAG TT - #TGGCTCGC     2580     - TATGCTTTTG ACTTTTATGA AGTTACATCA CGTACACCAG TGAGGGCTAG AG - #AGGCACAC     2640     - ATTCAAATGA AGGCCGCAGC TTTAAAATCA GCTCAATCTC GACTTTTCGG AT - #TGGATGGT     2700     - GGCATTAGTA CACAAGAGGA AAACACAGAG AGGCACACCA CCGAGGATGT TT - #CTCCAAGT     2760     - ATGCATACTC TACTTGGAGT GAAGAACATG TGATTGTAGT GTCTTTCCGG AC - #GATATATA     2820     - GATATTTATG TTTGCAGTAA GTATTTTGGC TTTTCCTGTA CTACTTTTAT CG - #TAATTAAT     2880     #    2917          TCCT CTAGAGTCCA CCTGCAG     - (2) INFORMATION FOR SEQ ID NO:4:     -      (i) SEQUENCE CHARACTERISTICS:     #pairs    (A) LENGTH: 75 base               (B) TYPE: nucleic acid               (C) STRANDEDNESS: unknown               (D) TOPOLOGY: unknown     -    (iii) HYPOTHETICAL: NO     -    (iii) ANTI-SENSE: NO     -     (vi) ORIGINAL SOURCE:               (A) ORGANISM: Primer     -     (xi) SEQUENCE DESCRIPTION: SEQ ID NO:4:     - TGTGGTACCG TCACCGGATG TGCTTTCCGG TCTGATGAGT CCGTGAGGAC GA - #AACGGTAT       60     #    75     - (2) INFORMATION FOR SEQ ID NO:5:     -      (i) SEQUENCE CHARACTERISTICS:     #pairs    (A) LENGTH: 73 base               (B) TYPE: nucleic acid               (C) STRANDEDNESS: unknown               (D) TOPOLOGY: unknown     -    (iii) HYPOTHETICAL: NO     -    (iii) ANTI-SENSE: NO     -     (vi) ORIGINAL SOURCE:               (A) ORGANISM: Primer     -     (xi) SEQUENCE DESCRIPTION: SEQ ID NO:5:     - ATAGGTACCG TTTCGTCCTC ACGGACTCAT CAGACCGGAA AGCACATCCG GT - #GACGGTCA       60     #      73     __________________________________________________________________________ 

I claim:
 1. A nucleotide sequence comprising a transcriptional regulatory sequence and a sequence contiguous therewith and under the transcriptional control thereof, which contiguous sequence encodes an RNA which consists of a plurality of sub-sequences, wherein at least two of the sub-sequences have the sequences of viral RNAs and the RNA contains at least one translational stop codon located upstream of the 3' terminal sub-sequence.
 2. A nucleotide sequence according to claim 1, wherein at least one of the sub-sequences is in an anti-sense orientation with respect to virus RNA.
 3. A nucleotide sequence according to either of claims 1 or 2, wherein the contiguous sequence encodes mRNA.
 4. A nucleotide sequence according to any one of the preceding claims, wherein at least one of the sub-sequences is a cistron.
 5. A nucleotide sequence according to any one of the preceding claims, wherein the RNA encoded by the contiguous sequence comprises at least one ribozyme between two of the sub-sequences.
 6. A nucleotide sequence according to any one of the preceding claims, wherein at least one of the sub-sequences encodes a viral coat protein or a viral nucleocapsid protein.
 7. A nucleotide sequence according to any one of the preceding claims, wherein the contiguous sequence encodes an RNA which comprises at least one sub-sequence obtained from viruses selected from the group consisting of tospoviruses, potyviruses, potexviruses, tobamoviruses, luteoviruses, cucmoviruses, bromoviruses, closteroviruses, tombusviruses and furoviruses.
 8. A DNA construct comprising the nucleotide sequence of any one of claims 1 to
 7. 9. A vector comprising the nucleotide sequence of any one of claims 1 to 7, or the construct of claim
 8. 10. A nucleotide sequence according to claim 6 wherein the sub-sequence encodes a viral nucleocapsid protein obtained from viruses selected from the group consisting of tomato spotted wilt virus, tomato chlorotic spot virus, groundnut ringspot, groundnut bud necrosis virus and Impatiens necrotic spot virus.
 11. A nucleotide sequence according to claim 6 wherein the sub-sequence encodes a viral coat protein obtained from a cucumber mosaic virus or a potato virus Y.
 12. The DNA construct according to claim 8, wherein the nucleotide sequence is SEQ ID No.
 1. 13. The DNA construct according to claim 8 wherein the nucleotide sequence is SEQ ID No.2.
 14. The DNA construct according to claim 8 wherein the nucleotide sequence is SEQ ID No.3.
 15. A plant cell containing the nucleotide sequence according to any one of claims 1 to 7, the construct of claim 8 or the vector of claim
 9. 16. A plant comprising the cells of claim 15, wherein the progeny of said plant includes the sequence stably incorporated therein and inhereditable in a Mendelian manner.
 17. The seeds of the plant and the seeds of the plant progeny according to claim
 16. 18. A method of producing a virus resistant or tolerant plant cell comprising the steps of introducing into a plant cell the sequence according to anv one of claims 1 to 7, the construct of claim 8, or the vector of claim 9, obtaining a transformed plant cell wherein the sequence, construct or vector is stably incorporated therein and said transformed plant cell is virus resistant or tolerant.
 19. A method of producing morphologically normal virus resistant or tolerant whole plants comprising the steps ofa. introducing into plant cells the sequence according to any one of claims 1 to 7, the construct of claim 8, or the vector of claim 9; b. obtaining transformed plant cells; and c. regenerating from the transformed plant cells genetically transformed plants wherein said transformed plants are morphologically normal virus resistant or tolerant whole plants.
 20. A method of inducing resistance or tolerance to viruses in plant cells comprising the steps of; a) introducing into said plant cells a nucleotide sequence according to any one of claims 1 to 7 or a construct according to claim 8 or the vector according to claim
 9. 21. A method of inhibiting the production of at least one enzyme in a plant cell comprising introducing into the said cell a nucleotide sequence comprising a transcriprional regulatory sequence and a sequence contiguous therewih and under transcriptional control thereof, which contiguous sequence encodes a RNA which consists of a plurality of subsequences, wherein the RNA encoded by the contiguous sequence contains at least one translational stop codon located upstream of the 3' terminal sub-sequence.
 22. A method according to the preceding claim, wherein at least one of the sub-sequences is in an anti-sense orientation with respect to the coding sequence in the host cell mRNA which encodes the said enzymne.
 23. A nucleotide sequence comprising a transcriptional regulatory sequence and a sequence contiguous therewith and under the transcriptional control thereof, which contiguous sequence encodes a mRNA which includes in the 5' to 3' direction (i) a translation start codon; (ii) a coding region selected from the group consisting of sequences encoding a nucleocapsid protein, a coat protein, and a viral replicase; (iii) a translation stop codon; (iv) optionally a second start codon; (v) a second coding region selected from the group consisting of sequences encoding a nucleocapsid protein in either the sense or antisense orientation, and a viral replicase; and (vi) optionally a second stop codon wherein the first coding region is translated and the second coding region is not translated as a result of the stop codon on the 3' side of the region encoding the second coding region.
 24. A nucleotide sequence comprising,(i) transcriptional regulatory elements and (ii) a sequence contiguous with the transcriptional regulatory elements and under control thereof,wherein the contiguous sequence encodes an RNA which consists of at least two sub-sequences and not more than seven sub-sequences and at least two of the sub-sequences have sequences of viral RNA which may encode a viral coat protein or a viral nucleocapsid protein and the RNA contains at least one translational stop codon located upstream of the 3' tennnal sub-sequence.
 25. The sequence of claim 24 wherein the nucleocapsid protein is a tospovirus nucleocapsid protein of a virus selected from the group consisting of tomato spotted wilt virus, tomato chlorotic spot virus, groundnut ringspot virus, groundnut bud necrosis virus and impatiens necrotic spot virus.
 26. The sequence of claim 24 wherein the coat protein is obtained from a cucumber mosaic virus or a potato virus Y.
 27. The sequence of claim 24 wherein at least one of the sub-sequences is a cistron. 